Industrial fabrics means endless structures in the form of a continuous loop, and used generally in the manner of conveyor belts. As used throughout this disclosure, “industrial fabrics” refers to fabrics configured for modern papermaking machines, and engineered fabrics, which may be used in the production of nonwovens. Modern papermaking machines employ endless fabrics/belts configured for use in the forming, pressing, and drying sections, as well as process belts such as shoe press or transfer belts, which may also be used in sections of the modern papermaking processes, such as in the pressing section. Engineered fabrics specifically refers to fabrics/belts used outside of papermaking, including use on preparation machinery for paper mills (i.e., pulp), or in the production of nonwovens, or fabrics used in the corrugated box board industries, food production facilities, tanneries, and in the building products and textile industries. (See, for example, Albany International 2010 Annual Report and 10-K, Albany International, 216 Airport Drive, Rochester, N.H. 03867, dated May 27, 2010.)
In the formation of industrial fabrics, the base structure or a component thereof may take a number of different forms. For example, the fabric may be woven endless or flat woven, and subsequently rendered into an endless form with a seam. Industrial fabrics, as endless loops, have a specific length, measured circumferentially therearound, and a specific width, measured transversely thereacross. In many applications, industrial fabrics must maintain a uniform thickness, or caliper, to prevent, for example, premature wear in areas where a localized thickness is greater than in the immediate surrounding area, or objectionable marking of a manufactured good carried thereon or contacted thereby.
Industrial fabrics used in modern papermaking machines and in the production of nonwovens may have a width from about 5 feet to over 33 feet, a length from about 40 feet to over 400 feet, and weigh from approximately 100 pounds to over 3,000 pounds, for example.
Because of their size and weight, and the configuration of the industrial machines on which they are used, in many applications it is often convenient to install industrial fabrics on the appropriate machine as a flat article having lengthwise and widthwise edges, and joining the widthwise edges with a seam, for example, to form a continuous belt. When installed flat and formed into a continuous loop structure on an industrial machine, such industrial fabrics may be known as on-machine-seamable fabrics.
Seams, however, have presented problems in the function and use of on-machine-seamable fabrics in that they may have a thickness, or caliper, that is different from that of the industrial fabric edges the seam is joining. Variations in thickness between the seam and the fabric edges can lead to marking of the product carried on the fabric. Seam failure may also result if the seam area has a greater thickness than the fabric edges as the seam is exposed to machine components and resulting abrasion or friction.
To facilitate seaming, many fabrics for industrial use have seaming loops formed on two opposite edges of the fabric to be joined. For example, seaming loops themselves may be formed from the warp yarns of a flat woven fabric. Seaming loops can be formed by removing weft yarns at the ends of the fabric to free end portions of warp yarns. Loops are formed by reintroducing (re-weaving) the free end portions of the warp yarns into the fabric.
A seam is formed by bringing the two ends of the fabric together, by interdigitating and alternating the seaming loops at the two ends of the fabric to align the openings in the loops to form a single passage, and by directing a pin, or pintle, through the passage to lock the two ends of the fabric together.
Alternatively, in one of the earliest uses of spiral link coils, a seaming spiral may be attached to the seaming loops at each of the two ends of an industrial fabric. An example of this method is shown in U.S. Pat. No. 4,896,702 to Crook in which a multilayer industrial fabric is formed. As shown, a tubular base fabric is formed, flattened to form edges at the lengthwise extremities of the fabric, and cross machine direction (“CD”) yarns in the area of the edges are removed. A spiral coil is attached to the seaming loops of the industrial fabric. Alternately, the seaming spirals may be connected to the seaming loops by at least one connecting yarn. The coils of the spirals at the two ends of the industrial fabric may again then be interdigitated and joined to one another on the machine with a pintle to form a seam usually referred to as a spiral seam.
Regardless of how the seam is formed, the construction of the seam differs from that of the rest of the fabric. Uniformity in characteristics such as permeability to air or water, thickness or caliper, and density, among others, is desirable in industrial belts. In known on-machine-seamable fabrics, construction of the seam area is different than the construction of the rest of the fabric. Because uniform physical characteristics across the length and width of the industrial fabric are usually preferred, and may be required, a seam is a critical part of a seamed fabric. If the seam itself is not structurally and functionally nearly identical to the rest of the industrial fabric, modification of the seam area may be necessary to obtain characteristics sufficiently similar to the main portion of the industrial fabric for the intended application.
One well known fabric, which has a body similar to the seam is the spiral link belt disclosed in U.S. Pat. No. 4,839,213 to Gauthier, for example. The '213 patent discloses a conveyor belt made of spirals assembled together by inserting rods into channels formed by interdigitating adjacent spirals. The belt includes a flat or other shaped member (known as “stuffer”) which is inserted inside the spirals so as to completely or partially fill the spaces inside the spirals. There are certain drawbacks of using such a belt, however. For example, the belt has a relatively stiff body due to the use of stuffers within the spirals to achieve the desired lower air permeability. Also additional expense, a separate process step to insert the stuffers, and additional mass are drawbacks. The spiral link coils, when made full width, can sometimes fail at one location and “unzip” across the CD when the belt is running on the machine, which can result in belt failure and significant damage to the paper machine components.
Another example of an industrial fabric is disclosed in U.S. Pat. No. 6,918,998 to Hansen, which relates to a fabric manufactured from preformed rings. The rings in the '998 patent are connected with MD or CD yarns, pintles or wires to form a flat fabric, whose ends are joined to one another to form a continuous loop. The rings disclosed in this patent are preferably manufactured from rigid materials, which make them relatively stiff and incompressible.
Therefore, a need exists for industrial fabrics, for example on-machine-seamable fabrics, which are easy to manufacture and have uniform characteristics throughout the length and width of the fabric.